聚焦光束粉末堆焊熔池的凝固特征及微观组织形成机理

采用OMI，SEM，EDS及XRD法研究了聚焦光束预涂粉末堆焊和送粉堆焊过程的熔池凝固特点，分析了堆焊层微观组织的形成机理，实验结果表明。大线能量光束堆焊层由底部具有外延生长特征的γ（Fe,Ni)平面晶及逆热流择优生长的γ（Fe,Ni)树枝晶组成，而且堆焊层表面树枝晶与光束扫描方向的夹角小于堆焊层底部树枝晶与光束扫描方向的夹角。送粉堆焊及预涂粉末堆焊层中的基底相均为γ（Fe,Ni)相，后析出的γ（Fe,Ni)富Cr。预涂粉末堆焊时堆焊层局部区域Cr,C元素的富集导致了Cr23C6析出。送粉堆焊过程中熔池过热度小，B，Si等造渣元素的烧损少。堆焊层中局部区域富集的B元素优先与Cr元素结合以Cr5B3形式析出。

SOLIDIFICATION CHARACTERISTICS OF MOLTEN POOL AND FORMATION MECHANISM OF MICROSTRUCTURE OF LIGHT BEAM SURFACING LAYER

The solidification characteristics of the molten pool and the formation mechanism of the microstructure during light beam surfacing process with pre -placed powder as well as powder feeding were investigated by using OM, SEM, EDS and XRD. Results indicate that the light beam surfacing layer with high energy input is consisted of epitaxially growing r(Fe, Ni) planar crystal in the bottom of the layer and r(Fe, Ni) dendrite which was growing opposite the heat flux with preferred orientation. The angle between the dendrite and the direction of light beam scanning in the top of the layer is smaller than that in the bottom of the layer. The matrix in the surfacing layer is r(Fe, Ni) phase and more Cr was contained in later formed r(Fe, Ni) phase. During the surfacing process, Cr23C6 was precipitated in the layer with the pre-placed powder, which was caused by Cr and C accumulation in local region, but Cr5B3 was precipitated in local region in the powder feeding surfacing layer, which was caused by lower loss of B and Si by less overheating.